In the USA, your airline is required to provide the wheelchair service free of charge. They can't say a certain gate doesn't have the service available.
Link to government website:
https://www.transportation.gov/indiv...ded-assistance

Now, reality has shown me that MANY times airports are understaffed and don't have enough people to push the wheelchairs, but that's a different story.

If you were not provided with the service required by US law, the link above includes the form to file a complaint. Here's that language (from the same page above) and the link directly to the complain form:
https://www.transportation.gov/airco...umer-complaintIf you believe your rights under the Air Carrier Access Act are being or have been violated, ask to speak with a Complaints Resolution Official (CRO). A CRO is the airline’s expert on disability accommodation issues. Airlines are required to make one available to you, at no cost, in person at the airport or by telephone during the times they are operating.
I hate to complain, and I hate that I require assistance these days, but difficult economies don't permit companies to break the law, and I feel like I'm better placed to complain (and nudge the airlines) than other passengers with fewer resources and less free time, so I always speak up on this issue.